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4/8/12
1
Evalua,ng Chemical Processes and Products
15 November 2011
Ch. 6 – Evalua,ng Feedstocks & Star,ng Materials
• Four factors 1. Origins – where is the feedstock from? 2. Renewable or deple,ng? – industry needs a
sustainable supply because scarcity increases costs.
3. Hazardous or innocuous? – Must consider acute and chronic toxicity, carcinogenicity, and ecotoxicity.
4. Downstream implica,ons – The en,re process must be considered.
Origins of feedstock
Can a waste byproduct from another process be u,lized?
O
O
O
O
O
O
NaOCH3CH3OH
O
OCH3
3
OH
OH
OH
+
PRODUCTION OF BIODIESEL:
triglyceride
transesterifica,on reac,on biodiesel
(methyl esters of fa\y acids)
glycerol
Produc,on of useful products from glycerol
• Every 9 kg of biodiesel produced results in the produc,on of approximately 1 kg of glycerol.
• Glycerol is produced in an amount about twice the demand.
• The American Oil Chemists Society began gran,ng the Glycerine Innova,on Research Award in 2003 to encourage research into applica,ons for the excess glycerol produced. – h\p://www.aocs.org/Membership/content.cfm?ItemNumber=804
Cann & Umile, The Prepara,on of Propylene Glycol from the Glycerin Byproduct of Biodiesel. Real‐World Cases in Green Chemistry, Vol. II, 2008, ACS.
Propylene glycol
• Propylene glycol has a significantly larger market than glycerol – nontoxic addi,ve for food and cosme,cs
• Currently, most of the supply comes from petroleum via the chlorohydrin process.
• Atom economy = 40%
Cl2
H2O Cl
OHNaOH
OH2O
120–190°C
high pressure
OH
OH
Propylene Glycol from Glycerol
• The Suppes process won the Glycerine Innova,on Research Award in 2005 and Presiden,al Green Chemistry Challenge Award in 2006.
• Atom economy = 81% • Byproduct is water • Dow commercialized the technology in 2007
OH
OH
HOcopper chromite
H–H, 200°C, 200 psi OH
OH
4/8/12
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Acetol forma,on
• Suppes and coworkers found that acetol was formed as an intermediate, and op,mized condi,ons for its synthesis.
• This is an interes,ng feedstock for more complex molecules and polymers.
OH
OH
HOcopper chromite
240°C, 14 psi OH
O
Produc,on of polymers from waste glycerol
• Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyacids.
• They can be biosynthesized by a number of organisms.
• Recently, organisms were modified to produce PHAs from waste glycerol from biodiesel produc,on.
O
HO
OH
3‐hydroxybutyric acid
Lu, et al., Mini‐Review: Biosynthesis of Poly(Hydroxyalkanoates). J. Macromol. Sci. Part C: Polym. Rev. 2009, 49, 226‐248. Wang & Nomura, Monitoring differences in gene expression levels and polyhydroxyalkanoate (PHA) produc,on in Pseudomonas puCda KT2440 grown on different carbon sources. J. Biosci. Bioeng. 2010, 110, 653‐659.
PHA bioproduc,on
• PHA is also biodegradable, so it could theore,cally be used in a closed cycle.
h\p://www.esf.edu/chemistry/nomura/lab/research/default.htm
Renewable Feedstocks
Polyethylene • Polyethylene (PE) is prepared by the polymeriza,on of ethylene (CH2=CH2).
High Density Polyethylene is a linear polymer prepared by a cataly,c process.
The polymer chains pack closely together to form a strong, rigid material.
Low Density Polyethylene is a branched polymer prepared by a free radical process.
The polymer chains are loosely packed to form a flexible material.
h\p://www.uline.com/ h\p://www.biztrademarket.com/
Sources of ethylene
Refining, cracking, etc.
petroleum
C C
H
H H
H
h\p://www.energyinsights.net/
h\p://www.climateark.org/
refining SUGARS
fermenta,on CH3CH2OH
dehydra,on
ethanol
biomass
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PlantBo\le
• The PlantBo\le is made of up to 100% plant‐based HDPE.
• It is iden,cal to petroleum‐derived HDPE.
• It can be recycled in the same manner as other HDPE.
• It is not biodegradable or compostable.
Renewable feedstocks
Poly(ethylene terephthalate)
• PET is a polyester prepared by a condensa,on polymeriza,on of ethylene glycol and terephthalic acid.
OH
O
HO
O
HO
OH+
O
O
O
O
O
ethylene glycol is prepared by dihydroxyla,on of ethylene.
PET is a clear, strong, flexible, impervious polymer.
h\p://earth911.com/
100% plant‐based PET bo\le
• In March 2011, Pepsi introduced an up to 100% plant‐based PET bo\le.
• They plan to use leiovers from their food business to produce the plas,c.
Is this really greener?
• There’s some debate. • Here’s what Coca‐Cola says: – h\p://www.thecoca‐colacompany.com/ci,zenship/plantbo\le.html
• Here’s what environmentalists say: – h\p://plas,csnews.com/blog/2011/04/environmentalists_blast_cokes.html
What about a renewable and biodegradable polymer?
• NatureWorks polylac,c acid is prepared from renewable feedstock.
Cann & Umile, Development of NatureWorks Polylac,c Acid, A Polymer Derived from Annually Renewable Resources. Real‐World Cases in Green Chemistry, Vol. II, 2008, ACS.
starch glucosefermentation
enzymatic hydrolysis HO
OH
O
lactic acid
condensation (–H2O)
HOO
O
H
prepolymer (low MW)
catalytic depolymerization
O
O
O
Olactide
catalytic ROPHO
O
O
H
PLA (high MW)
4/8/12
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PLA is fully biodegradable
h\p://www.packaging‐int.com/ h\p://www.ilip.it/en/no,zie_060912.asp
PLA has superior proper,es and can replace polystyrene (PS) and PET as food packaging.
Innocuous feedstocks
• If the ini,al feedstocks are less hazardous, then the process and final product are oien less hazardous as well.
• If a less hazardous feedstock requires a more hazardous auxiliary substance during the manufacturing process, then it may not be beneficial.
• Example: Corrosion Preven,on
Corrosion preven,on
• Corrosion costs U.S. consumers $276 billion/year.
• Corrosion of motor vehicles costs $23.4 billion/year. – Increased manufacturing costs ($2.6 billion/year)
– Repairs and maintenance ($6.5 billion/year)
– Corrosion‐related deprecia,on ($14.5 billion/year)
Cann & Umile, Y\rium as a Lead Subs,tute in Electrodeposi,on Coa,ngs. Real‐World Cases in Green Chemistry, Vol. II, 2008, ACS.
www.corrosioncost.com (archived July 2011)
What is corrosion? • When a metal becomes oxidized, the resul,ng oxide may be
more soluble and wash away. • Oxida,on of a metal is always accompanied by a reduc,on
reac,on, usually of water or ambient oxygen.
2 Fe 2 Fe2+ + 4 e– O2 + 2 H2O + 4 e– 4 OH– 2 Fe2+ + 4 OH– 2 Fe(OH)2
2 Fe + 2 H2O + O2 2 Fe(OH)2
4 Fe(OH)2 + O2 2 Fe2O3•H2O + 4 H2O
oxida/on
reduc/on
forma/on of salt
NET REACTION
forma/on of rust
Corrosion resistance
• Three ways a metal object can be made resistant to corrosion: 1. Adsorb a substance onto the surface of the
metal to shield it from the environment. 2. Apply a metal that is more easily oxidized than
the metal one wishes to protect. 3. Passiva,on – promote the forma,on of a thin
layer of insoluble metal oxide to protect the metal.
Shielding the metal
• The Golden Gate Bridge is painted to protect the metal from corrosion.
• What’s in the paint?
• When the bridge was first built in the 1930s, it was painted with a Pb‐based paint (Pb3O4 is red).
• In 1968, the paint began to be replaced with a zinc silicate primer and vinyl topcoats that retained the red color.
• In the 1990s the topcoat was changed to acrylic to meet air quality standards.
www.wikipedia.com
h\p://goldengatebridge.org/research/factsGGBIntOrngPaint.php
4/8/12
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How does passiva,on work?
• Pb3O4 reacts with the iron to form a thin insoluble surface coa,ng that protects the remaining iron from rus,ng.
• Another method is electropla,ng Zn onto the metal surface (galvaniza,on); however, this is too expensive for large automobile components.
Electrodeposi,on • Electrodeposi,on allows for a thin, uniform coa,ng of a metal to be applied to the surface of another metal.
• The metal to be coated is the cathode, and that to be deposited is the anode.
• When a voltage is applied, the anode metal migrates and deposits onto the cathode.
www.wikipedia.com
Using Y\rium as an Innocuous Feedstock
• Y\rium is abundant, inexpensive, and nontoxic • Electrodeposi,on of y\rium onto an iron surface results in the forma,on of insoluble y\rium‐iron‐oxide compounds that protect the underlying iron from corrosion.
• Es,mated to remove 1 million pounds of Pb per year from automo,ve products. Also reduces the use of chromium and nickel that are required for the Pb‐based process.
• PPG Industries won a Presiden,al Green Chemistry Award for this development in 2001.
Greening Dry Cleaning
• Supercri,cal CO2 has begun to replace PERC as the solvent of choice for dry cleaning.
• This work won A Presiden,al Green Chemistry Award in 1997.
Ch. 7 – Evalua,ng Reac,on Types
• Some types of reac,ons are inherently more efficient than others.
• Recall the defini,on of atom economy:
• Atom economy describes the amount of reactants that end up in the products.
% Atom economy = FW of atoms utilized
FW of all reactants used
Trost, B. M. The Atom Economy–A Search For Synthe,c Efficiency. Science, 1991, 254, 1471‐1477.
Rearrangement Reac,ons
• 100% atom economy • Example: Claisen rearrangement
• Reac,on is driven by strength of the C=O bond compared to C=C bond.
Oheat O
4/8/12
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Addi,on Reac,ons
• Simple addi,on reac,ons are 100% atom economical.
• Addi,on reac,ons are oien regioselec,ve and stereoselec,ve, increasing their synthe,c u,lity.
• Oien, however, addi,onal reagents are required.
HBr Br
Subs,tu,on Reac,ons
• Atom economy depends on nature of nucleophile and leaving group.
• Small nucleophile and large leaving group: CH3I + NaCl CH3Cl + NaI – Atom economy = 25%
• Large nucleophile and small leaving group: CH3Cl + NaI CH3I + NaCl – Atom economy = 71%
Elimina,on Reac,ons
• Can have very poor atom economy, since the molecule fragments.
• E2 requires stoichiometric use of base.
• Atom economy = 35%
Br
NaOEt+ EtOH + NaBr
Pericyclic Reac,ons
• Can be addi,ons (100% atom economy) – Diels‐Alder
• Can be rearrangements (100% atom economy) – Cope rearrangement
• Can be elimina,ons (usu. poor atom economy) – retro‐Diels‐Alder
Oheat O
Oxida,on‐Reduc,on Reac,ons
• Atom economy varies depending on actual reac,on condi,ons.
• Oien, toxicity of reagents outweighs atom economy considera,ons.
OH O
H
PCC
CH2Cl2
PCC = pyridinium chlorochromate- carcinogen- toxic
NH CrO3Cl
CH2Cl2 = dichloromethane- toxic to multiple physiological systems
Alternate condi,ons
• Swern oxida,on
• This reac,on is more tolerant of other func,onal groups, minimizing the need for protec,on/deprotec,on and other auxiliary substances.
OH O
H
1. oxalyl chloride, DMSO
2. triethylamine
oxalyl chloride- corrosive to skin and other tissues
DMSO- relatively nontoxic
triethylamine- toxic to kidneys and liver, high LD50
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Other considera,ons
• What auxiliary reagents are required? – What is their quan,ty and toxicity?
• What are the “planned” byproducts? – These are fundamental to reac,on type and can only be eliminated by changing the sequence of reac,ons that lead to a product.
• What are the “unplanned” byproducts? – These are a result of side reac,ons and can some,mes be eliminated by altering reac,on condi,ons.
Ch. 8 – Evalua,on of methods to design safer chemicals
• Usual ques,on: What is the desired func,on of the product?
• This is an incomplete ques,on – it is also necessary to mi,gate toxicity and other hazards.
• The goal is performance with minimal hazard.
• How can we go about designing safer chemical products and processes?
Designing safer chemicals
1. Understand mechanism of ac,on 2. Structure‐Ac,vity rela,onships 3. Avoid toxic func,onal groups 4. Minimize bioavailability 5. Minimize auxiliary substances
Understand Mechanism of Ac,on
• If the mechanism of toxicity is known, a chemical substance can be altered so that the mechanism cannot take place.
• Example: new insec,cides
Insec,cides • Many tradi,onal chlorinated insec,cides are bioaccumula,ve, environmentally persistent, and toxic.
• Alterna,ves, such as organophosphates and carbamates, are acutely and chronically toxic to humans and other organisms.
Cann & Connelly, The Inven,on and Commercializa,on of a New Chemical Family of Insec,cides Examplified by CONFIRM Selec,ve Caterpillar Control Agent and the Related Selec,ve Insect Control Agents ACH 2 and INTREPID. Real‐World Cases in Green Chemistry, 2000, ACS.
Cl ClCl
Cl Cl
DDT
S
PMeO
MeOS
O OEt
O OEt
Malathion
O O
NHCH3
carbaryl (Sevin)
New insec,cides – mol,ng inhibitors
• Rohm & Haas developed a new class of insec,cides that inhibit mol,ng in caterpillars and other larvae.
• When mol,ng is suspended, the caterpillar cannot shed its cu,cle, and stops ea,ng.
• The new insec,cides have reduced risk to humans and non‐target species.
• These insec,cides received a 1998 Presiden,al Green Chemistry Award.
4/8/12
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Diacylhydrazine mol,ng inhibitors
• Mul,ple insec,cides have been developed, each of which targets a par,cular class of insects.
NH
O
N O
Tebufenozide – targets lepidoptera caterpillars
Cl
NH
O
N O
Halofenozide– targets beetle larvae and turf grubs
Structure‐Ac,vity Rela,onships
• If the exact mechanism of ac,on is unknown, it is s,ll possible to establish quan,ta,ve structure‐ac,vity rela,onships (QSAR).
• The structure is changed in some way, and the new toxicity measured.
• The informa,on can help with designing less toxic chemical products. – h\p://www.epa.gov/nrmrl/std/cppb/qsar/
Avoid toxic func,onal groups
• Even if mechanisms and QSAR rela,onships are unknown, it is some,mes possible to eliminate the func,onal group responsible for the toxicity.
• If that func,onal group is required for the func,on of the molecule, it can be masked for handling and unmasked for use.
• Example: trans fats in food
Elimina,ng trans fats • Par,al hydrogena,on of unsaturated oils raises their mel,ng points and increases shelf life.
• Tradi,onal hydrogena,on uses H2 with a catalyst.
Cann & Umile, Healthier Fats and Oils by Green Chemistry: Enzyma,c Interesterifica,on for Produc,on of No trans‐Fats and Oils. Real‐World Cases in Green Chemistry, Vol. II, 2008, ACS.
O
O
O
O
O
(CH2)7CH=CH(CH2)7CH3
(CH2)7CH=CH(CH2)7CH3
O
(CH2)7CH=CH(CH2)7CH3
H2
catalyst
O
O
O
O
O
(CH2)16CH3
(CH2)16CH3
O
(CH2)16CH3
triolein
mp –4 °C
tristearin
mp 72 °C
Par,al hydrogena,on
• Naturally occurring unsaturated fa\y acids contain over 99.5% cis double bonds
• Par,al hydrogena,on results in the conversion of 30‐40% of these to the trans configura,on.
• trans fats raise levels of LDL cholesterol, leading to heart disease.
cis trans
Interesterifica,on
• Interesterifica,on results in mixing the side chains of triglycerides to produce a mixture with an intermediate mel,ng point between the two star,ng fats.
O
O
O
O
O
(CH2)7CH=CH(CH2)7CH3
(CH2)7CH=CH(CH2)7CH3
O
(CH2)7CH=CH(CH2)7CH3
O
O
O
O
O
(CH2)16CH3
(CH2)16CH3
O
(CH2)16CH3
new triglyceride mixturemp between –4 and 72 °C
4/8/12
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Interesterifica,on
• Chemical interesterifica,on uses strong bases such as sodium methoxide.
• It is too expensive to do on a large scale. • Novozymes and Archer Daniels Midland Company shared a Presiden,al Green Chemistry Award in 2005 for the development of Lipozyme TL.
Benefits of new enzyme
• Lower cost • No caus,c chemicals required
• No byproducts, so less waste
• Less wastewater, and no solid waste produced
• Specific to 1‐ and 3‐posi,ons of triglyceride
h\p://portal.aniame.com/ar,culo_58.shtml
Minimize bioavailability
• One approach to dealing with toxicity is to design molecules so that entry into the biological system is either impaired or eliminated.
• Examples: a\ach the substance onto a polymer or other solid support
Polymer‐supported reagents
• Cyanoborohydride is used for reduc,ve amina,on.
• The reac,on produces CN– as a byproduct. • Immobilizing the reagent on a polymer removes the cyanide ion from solu,on, making the reac,on safer.
OR-NH2
NaBH3CN
NH
R
h\p://www.erowid.org/archive/rhodium/pdf/solid‐supported.reagents.pdf
Minimize auxiliary substances
• Where toxici,es are unknown, it is best to minimize the amount and number of auxiliary substances in order to minimize the possibility of hazard.
Summary
• Green chemistry can be evaluated in several ways: – How green are the star,ng materials? – How efficient are the reac,ons? – How safe are the processes and products?
4/8/12
10
Homework
• Wri\en assignment: Ch. 6 #1‐3, Ch. 7 #1‐3, Ch. 8 #1 & 5 – Possible reac,ons for Ch. 7 ques,ons: • Diels‐Alder • Wizg Reac,on • Freidel‐Crais Acyla,on • Oxymercura,on‐Demercura,on • Bromina,on of an alkene • PCC oxida,on • Swern oxida,on
Short Presenta,on
• Choose a product that claims to be “green” and evaluate those claims – Inves,gate the chemistry – Determine which of the 12 principles are being applied by the designer and/or manufacturer
– Would you give this company a Presiden,al Green Chemistry Award? – see selec,on criteria here: • h\p://www.epa.gov/greenchemistry/pubs/pgcc/select.html
Award Selec,on Criteria
1. Science and innova,on – Must be original and scien,fically valid.
2. Human health and environmental benefits – Should offer these benefits at some point in its
lifecycle.
3. Applicability and impact – Must be prac,cal and commercially viable, and
solve a real problem.
Final Project
• Time permizng, you may wish to begin working on the wri\en summary of your final project topic.
• Three sec,ons: – Overview – Problem – Solu,on (this may be incomplete depending on your chosen topic)